This invention relates to printed-circuit board assemblies and in particular, to structures for electrically connecting components with a minimum of parasitic inductance.
A single-sided printed-circuit board generally consists of a fiberglass substrate having a component-side and a solder-side. On the solder-side, conducting paths are imprinted or deposited. On the component side, various electrical components are mounted and connected to the conducting paths on the solder-side through strategically located through holes.
It is well-known in electromagnetic theory that a current on a conducting path will support a magnetic field. It is also well-known that a magnetic field abhors change. When the current that supports it is suddenly removed, a magnetic field will attempt to restore the status-quo by expending some of its own stored energy to cause the flow of an induced current to replace the current that was suddenly taken away. Because the magnetic field has only finite energy stored within it, this attempt is doomed to failure. Nevertheless, the magnetic field""s attempt to survive causes difficulty in a high-power switching circuit in which one would like to turn current on and off immediately.
The magnetic field""s propensity to resist change by inducing current in a conducting path is measured by inductance of that path. Because of its undesirable effect, this inductance is often referred to as a xe2x80x9cparasitic inductance.xe2x80x9d The inductance of a conducting path depends in part on the geometry of the path. In particular, by widening the conducting path one can reduce its parasitic inductance. However, in a printed-circuit board, there are practical limits to how wide a conducting path can be. As a conducting path becomes wider, portions of it necessarily become closer to other conducting paths and components on the same board.
Although it is possible to circumvent the foregoing difficulty by simply enlarging the printed-circuit board, this solution has several disadvantages. A larger printed-circuit board, particularly one large enough to accommodate several transistor modules in a power-switching circuit, is more expensive. In addition, a larger printed-circuit board undergoes greater deformation when placed under tension or compression or when thermally stressed. These deformations can weaken soldered connections on the printed-circuit board.
The invention provides a low-inductance connection between a first component and a second component on a first printed-circuit board by expanding into a third dimension and providing a second, auxiliary conducting path on a surface separate from the first printed-circuit board. This separate surface is spaced apart from the first printed-circuit board and therefore does not occupy additional area on that printed-circuit board.
The low-inductance connection includes a first conducting path disposed on a first surface of the first printed-circuit board and extending between the first component and the second component. The connection also includes a second conducting path disposed on a separate surface that is separated from the first printed-circuit board. The second conducting path is in electrical communication with the first conducting path. The first and second conducting paths thus cooperate to effectively act as a wide conducting path having a lower parasitic inductance than that of the first conducting path acting by itself.
Typically, the second conducting path is disposed on a second printed-circuit board having a proximal surface facing the first printed-circuit board and a distal surface opposite the proximal surface. The surface on which the second conducting path is disposed can be the distal or proximal surface of the second printed-circuit board. Alternatively, the second conducting path can be disposed on a second surface of the first printed-circuit board.
The insulating layer between the first and second conducting paths can be an air-filled gap or a gap filled by an insulating gas. Alternatively, the insulating layer can be a layer of a dielectric material. When the second conducting path is disposed on the distal surface of the second printed-circuit board, the dielectric material is the material used for making the second printed-circuit board. When the second conducting path is disposed on a second surface of the first printed-circuit board, the dielectric material is the material used for making the first printed-circuit board.
By making use of an area of the printed-circuit board that is otherwise unused, the invention provides a low-inductance connection between two electrical components of a printed-circuit board without requiring an enlargement of the printed-circuit board. These and other features of the invention will be apparent from the following detailed description and the accompanying figures, in which: